The present invention relates to an inspection device of magnetore-sistive head for checking output characteristics of the magnetoresistive head having a magnetoresistive element.
The magnetoresistive head, commonly used as a playback transducer for reading out information recorded on a magnetic medium, detects signals by way of magnetoresistive effect, that is, change in electric resistance of a ferromagnetic film, such as permalloy, caused by change in intensity of the external magnetic field.
The magnetoresistive head is advantageous compared to inductive magnetic heads, since, its resistance changing proportional to the magnetic field intensity independent of its relative velocity to the magnetic medium, a high output can be expected therewith. It also can be suitably applied for reproducing heads of hard disk drives where compactness and high recording density are required, as the magnetoresistive head can be highly integrated and easily prepared into multiple-elements by applying fine processing technology of the semiconductor manufacturing.
There is developed also a merged type head, wherein a magnetoresistive head and an inductive thin film head are combined for providing compactness and accurate mutual alignment of read/write heads towards recording tracks. The inductive thin film head means here a recording head element with its magnetic core and coil windings formed in thin film by way of the fine processing technology of the semiconductor manufacturing. In such a merged type head, a high reproducing voltage is ensured by applying magnetoresistive film of single magnetic domain to the magnetoresistive element for sensing magnetic field from the recording media.
However, the single domain of magnetoresistive film is sometimes broken due to stresses or distortions accompanying finishing processes of the magnetoresistive head, which causes a fluctuation in reproducing signals of the magnetoresistive head called the Barkhausen noise, degrading playback reliability of the magnetoresistive head.
Particularly, the magnetoresistive film is easy to receive partial stresses from slider finishing works performed in the Head-Gimbal-Assembly (hereafter abbreviated as the HGA) process of the magnetoresistive head, wherein slider surface facing to recording media is lapped. As a result, even with the magnetoresistive film confirmed before the HGA process to be a wafer of single domain generating no Barkhausen noise, there may be found the Barkhausen noise after the HGA process, because of the break of the single domain with the partial stresses of the magnetoresistive film.
Therefore, the Barkhausen noise of magnetoresistive heads should be evaluated after the HGA process.
FIG. 6 is a block diagram illustrating a conventional method for detecting the Barkhausen noise described in a Japanese patent application laid open as a Provisional Publication No. 187620/'94, wherein response characteristics of a magnetoresistive head is measured by applying thereon an external uniform magnetic field generated by an air-core coil, Helmholtz coil, for instance.
In FIG. 6, an external uniform magnetic field 62 is generated by an alternating current Ic flowing in an air-core coil 61 supplied through a constant-current amplifier 41 generated by an oscillator 42. A magnetoresistive head 10 responds to the external uniform magnetic field 62 applied thereon vertically to its surface facing to recording media.
Intensity of the alternating current Ic is converted into voltage value by a resistor 64 to be supplied to an oscilloscope 31 as an X-axis-input. Relation of the alternating current Ic to the external uniform magnetic field 62 is beforehand obtained by measuring the external uniform magnetic field 62 by a gaussmeter, for example. A sense current Is is supplied from a constant-current source 53 into a magnetoresistive element 11 of the magnetoresistive head 10. Output of the magnetoresistive head 10 is amplified by an output amplifier 51 and supplied to a first Y-axis-input terminal of the oscilloscope 31 for displaying characteristic curve thereof in X-Y display mode.
The output level of the magnetoresistive head 10 is optimized at the best operational point on its characteristic curve by controlling a bias current Ib flowing through a bias conductor 13 provided in the magnetoresistive head 10 supplied by a controllable constant current source 59. The output of the magnetoresistive head 10 is also supplied into a second Y-axis-inpiit terminal of the oscilloscope 31 after its fundamental frequency component is eliminated through a differential and filtering circuit 52.
When there is no Barkhausen noise produced in the magnetoresistive element 11 of the magnetoresistive head 10 responding to the external uniform magnetic field 62, no fluctuation is observed in the wave form of the second Y-axis-input of the oscilloscope 31 corresponding to the output through the differential and filtering circuit 52 without fundamental frequency component, as it is varying according to alternating current Ic generating the external uniform magnetic field 62.
When there is some Barkhausen noise because of the magnetoresistive element 11 having not single domain, they make fluctuations corresponding thereto independent of the X-axis-input, in the wave form of the second Y-axis-input.
Thus, the Barkhausen noise is checked in the conventional method.
However, there are following problems in the conventional method.
First, the Barkhausen noise in a frequency range where the magnetoresistive head 10 is actually used for read/write of recording media can not be checked, because the air-core coil 61 can not generate sufficient strong external uniform magnetic field 62 in such a high frequency range. Therefore, another Barkhausen noise measurement must be performed after the magnetoresistive head 10 is put together into a hard disk drive. This is a demerit for the mass-productivity.
Second, the Barkhausen noise caused by a magnetic field not uniform such as that originated from a micro portion of recording media can not be checked, because the air-core coil 61 can not apply diagonal magnetic field components to the magnetoresistive element 11 but a normal uniform magnetic field 62. Therefore, magnetoresistive heads 10 to be used for high recording density hard disk drives can not be checked with sufficient reliability.
Third, Barkhausen noise measurement considering spacing between the magnetoresistive head 10 and the recording media can not be performed, because it is performed in a uniform magnetic field 62 generated by the air-core coil 61.